Hi Allen, Diversification applies to your total portfolio not to a particular account. Besides, in a small account going with an ETF you'll be more diversified that by holding a couple of stocks.
As far as how age affects choice of portfolio, as you get older you want to stick with safe investments. True you have less time to make a killing but also less time to recover from bad investment. It's especially true in an IRA because you can't take a tax loss when the stock takes a dive.
You're much better off AIMing ETFs with the AIM-High 20% cash as suggested by Ray, than taking risks AIMing individual stocks. Remember, AIM is really a souped up form of dollar cost averaging, and that method is designed for investing in funds not individual stocks. When a stock goes into a dive it's foolish to keep dumping in money and buying more stock.